Motors have been developed that convert a wide variety of energy input into mechanic output. For example, internal combustion engines use explosion of combustible fuel to generate output. Likewise, steam and electric motors have been developed. One type of electric motor converts electricity to ultrasonic vibration and then to mechanical movement. The ultrasonic motor has a driving force generated by exciting a flexual vibration in a vibrating body comprising a piezoelectric element.
A representative example of a prior art ultrasonic motor is described with reference to FIGS. 1 and 2 and U.S. Pat. No. 5,448,129. FIG. 1 is a partially cut perspective view showing essential parts of a conventional ring-shaped ultrasonic motor. A reference numeral 103 denotes a vibrating body comprised of a ring-shaped elastic base 100 with plural projections 100a and a ring-shaped piezoelectric element 102 attached to the bottom surface of the elastic body 100. A reference numeral 106 denotes a moving body, which is comprised of a ring-shaped elastic body 104 with an abrasion resistant friction member 105 attached thereto. In this example of a conventional ultrasonic motor, steel or a stainless steel is usually used for the materials of the elastic body 104, and the friction member 105 is bonded thereto with an adhesive or other means.
The operation of the conventional ring-shaped ultrasonic motor thus comprised is described below with reference to FIG. 2, which shows that the moving body 106 and vibrating body 103 are held in pressure contact, and a progressive wave of flexural vibration is excited in the vibrating body 103. The progressive wave of flexural vibration is generated as follows. At first, a longitudinal vibration is caused in the piezoelectric element 102 by applying two AC voltages with a predetermined phase shift to two sets of driving electrodes arranged thereon. Since the elastic base 100 works to resist this longitudinal action, a progressive wave of flexural vibration is set up in the vibrating body 103. Any given point on the surface of the vibrating body 103 follows an elliptical motion due to the progressive wave of flexural vibration. The projections 100a enlarge the lateral displacement of this elliptical motion. The moving body 106, pressed in friction contact with projections 100a of the vibrating body 103, is rotationally driven due to the enlarged lateral displacement.
Prior art ultrasonic vibration motors use relatively complicated means of friction coupling a vibration source to the moving body. For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for an improved vibration driven motor.